Engine Rattling at high RPM and low throttle?

504 Views 20 Replies 6 Participants Last post by SparkyMJ, 13 d ago

SparkyMJ

Discussion Starter · 24 d ago

Hey folks,

Just wanna run this by some of you experienced folk.

K4 750 with 51k miles on it, and I've installed a PSR MCCT and done the valve adjustment. Engine internals look quite good, nothing visually alarming or showing a need to be replaced.

I installed the PSR MCCT after riding the bike a bit on the stock one. With the stock CCT there was some valve train noise at cold start idle, but idle would be totally normal once up to temp. This is the same with my MCCT. I initially set it too tightly to try and eliminate that noise at cold start idle, but I think it was too tight then because I think I heard the characteristic 'whirring' when it was too tight. Since then, it runs great and makes no excessive noise at any RPM under 6 or 7k, so normal driving it sounds perfect.

The noise at cold start I am not worried about, it goes away and all is fine. But I do have what sounds like valvetrain clattering only at high RPM. Say from 7k to redline. Less noticeable or less present when on the throttle hard or full throttle, and not due to exhaust noise drowning out the valvetrain noise. But say when I am in a corner at high RPM, and when I cracked the throttle open and gradually open it, that is when the clattering is most noticeable.

It sounds like a uneven clattering, not like valvetrain clockwork sounds. Also, it happens at a standstill, and if I clutch in at any speed it goes away of course.

Think I should tighten the MCCT more? I recently tightened it a small amount, and I am uncertain if it made a difference in the noises I am hearing. Maybe it is just a bit more loose, I think when I set it too tight before, it was a lot tighter than it is now.

Anything else that might make this uneven clattering noise? Engine mounts are good, no loose fairings or other bits, and the clattering sound is definitely metallic, and coming from under the tank. Tank rubber mounts are good too.

Bike runs fantastic. Just did it's first track day yesterday and it didn't skip a beat.

What do you guys think?

-Mike

See less See more

1 - 20 of 21 Posts

boostenlebaron

· #2 · 24 d ago

Switch oils next change and see if that helps. At 51k I would be running a 10w40 or 15w40.
I would lift the tank and see if I could pin point it better when revving. Maybe take the airbox off too but the intake noise may hide the sounds.
It could be your cam chain guides making that noise. If you still have the factory auto cct I would pop it in and see if it makes a difference.

SparkyMJ

Discussion Starter · #3 · 24 d ago

Thanks for the tips.

I run 10w-40 in it, and here in the PNW temperatures are pretty moderate.

The intake noise is quite fun on this bike but yeah it may make it hard to differentiate sounds.

I do have the factory auto CCT, but I might have lost the oil jet that is needed for it to work right...

I did make a small adjustment recently like I said and I think it did quiet down a hair. Maybe I will try another small adjustment and see if it makes another small difference in the sound. When I had the characteristic whirring sound, I think it was way tighter than it is currently.

This works out too, I think tomorrow I am going to my buddy's place to do a throttle sync, so I will have the tank up and the engine running then, I can listen to it again.

When I had the engine open the guides visually looked okay and the chain wasn't stretched much and the sprockets looked good. The guides might be worn and it is just not visually apparent, but I don't think they were too bad. My Ninja has worse looking cam chain guides at 60k miles and it runs and sounds great with the MCCT as well, for what it's worth.

Thoughts?
-Mike

See less See more

SparkyMJ

Discussion Starter · #4 · 23 d ago

I tightened the MCCT today a bit and found maybe a tiny difference. Maybe it is related. It was really hard to hear over the intake sound today when adjusting the tension, and when I took it out for a ride I tried to listen to the clattering sound really closely. It does seem to come and go as the RPMs go up and down, so maybe it is just some fairing piece or something vibrating... Engine still runs great. I did a throttle sync and that was nice to have done, it runs a little smoother now.

Maybe my valve guides are worn or something similar? I can't think of much else that might cause little to no power loss but just make noise from the top of the engine.

I think after this season, I will strip down the engine and do a full valve job and have a machine shop do any necessary cuts. Couldn't hurt.

-Mike

boostenlebaron

· #5 · 23 d ago

Have you checked the prices of new valves for your model recently? That could certainly hurt.

Grab a piece of tubing and use it as a make shift stethoscope and poke it around the motor. It will help locate the area at least. I still think a different oil is the best course of action right now though. I use rotella T.

SparkyMJ

Discussion Starter · #6 · 23 d ago (Edited)

I may give another oil a shot, but I just can't see that eliminating this noise.

I bet valves and guides are very expensive - but I also think that since my motor runs so well, maybe there are only a few having trouble. Or maybe my valve springs are just old, and that is why the motor runs dead smooth under 7k. I've never had to replace valve springs, but there could be a first for everything I suppose.

I am more looking to do the service than justify a financial decision too. If I can spend a thousand bucks and learn what worn valve train components look, sound, and act like, I think that is still worth doing. That said, I don't want to waste any money on valve train parts I don't need. My motor doesn't burn a drop of oil, so I am inclined to believe my valve seats and oil seals must be in decent shape.

I suppose the best way is to eventually just get in there and start measuring stuff... The shop book does have a valve spring inspection, and it does say that worn valve springs often cause "chattering of the valve mechanism". Valve springs are also relatively cheap compared to entirely new valves or guides. Might be worth getting a full set of springs and doing piston rings while I am in there. Thoughts?

Ever heard or felt what worn out valve springs is like?

-Mike

See less See more

TwistedMister

· #7 · 21 d ago

oil, make sure the top end is getting lubed, maybe check oil pressure

SparkyMJ

Discussion Starter · #8 · 21 d ago

Well some new things came out of this.

Yesterday at the track, the bike had had enough. Did the morning sessions with no issue, but the power delivery felt a bit weird at times. Come time to fire back up for afternoon, I was scrubbing in a new tire on track and after a slow lap I was ready to get on it, and there was zero power and a ton of vibration and noise above 7k. I couldn't get above say 8k.

No check codes, not overheating, had oil and coolant. Bike ran and sounded fine below 7k, plenty of grunt and torque still too. Idles fine, rode totally normal at mid to low RPMs. So I finished a lap or two and came in to the pits to retire for the day.

My buddy thinks the valve springs have lost their tempering/strength, and that the heat soak from the morning sessions was their final breath. Would make sense since it runs totally normal at low RPM, fires right up, doesn't smoke out the pipe, etc. The failure also wasn't immediate, like I said, it ran a little funky in the morning but not nearly as bad. No sudden snapping or sudden power loss, so probably not jumping timing, dropping a valve, interference collisions, or anything like that.

I also think it could possibly be a fuel issue, so I was going to do the fuel flow test before ripping the motor apart just in case, but I am pretty sure it isn't that. But worth at least sanity checking before pulling my motor apart.

If that looks to be alright, then I think I will just drop the motor and pull the head off, and see what I find.

You guys think I should do piston rings and a hone while I am in there? The motor doesn't consume a drop of oil though. Maybe only if I find scoring on the cylinder walls.

Thoughts?
-Mike

See less See more

Clipper

· #9 · 21 d ago

I'm struggling to buy the weak springs argument having done a full track day yesterday on mine with over 90k kms on it. Could be though.

Have you done a comp test? That would be my first port of call.

alexei

· #10 · 20 d ago

SparkyMJ said:
It sounds like a uneven clattering, not like valvetrain clockwork sounds. Also, it happens at a standstill, and if I clutch in at any speed it goes away of course.

Do you mean if you clutch in and rev freely, the noise does not occur?
Another guess would be the timing chain skipped, or something is wrong inside the intake manifold.

SparkyMJ

Discussion Starter · #11 · 20 d ago

It always rattled, moving or not, clutch in or not, neutral or not.

I got the engine out today and took the head off. Even if this isn't my issue, I think the valve springs are meant to be done.

There is no signs of valves hitting pistons or any other catastrophic damage at all. Cylinder walls look really good, combustion chambers looked normal, camshafts and lifters look good. No evidence of oil starvation anywhere, so I don't think that is my issue. Timing wasn't jumped either.

To be positive, I will measure the valve spring length and tension and see if they are out of spec. If they are, then that is pretty clearly my issue. If not, then I will start pulling hairs out. I am pretty sure that is what I will find though given the circumstances.

I have not tested the fuel pump yet. I know I should have first, but I am willing to lose the money on the valve springs regardless of the fuel pump flow test results. I am 98% sure my fuel pump wouldn't suddenly fail right also when my engine first cooled down after the hottest track sessions it has ever seen, but, indeed I will do the flow test here soon just to be sure.

Regardless, I think my intake boots were a tad leaky too, so I will remedy that while I am in here too, among a few other bits. The shop manual for the bike says my exact symptoms could be caused by weak valve springs. I think my valve springs were probably weakened by abuse from the previous owners. Because @Clipper I think you are right, the mileage isn't the problem here. I bet the previous owner just banged off the rev limiter a lot and did other bad stuff. I am going to check the valve seat dimensions and see if I can get a shop to seal test or take any other measurements while I've got it off.

I'll let you guys know what I find!

-Mike

See less See more

Reactions: 1

BillV

· #12 · 20 d ago

Any chance that your secondary throttle isn't opening as it should? I assume that you never saw a C28 or C29 error but am wondering if something like a dead zone in the secondary sensor would be detected. It should be fairly easy to check that the sensor resistance varies smoothly as the secondary is opened and closed.

SparkyMJ

Discussion Starter · #13 · 20 d ago

I already did the STVA circuit board mod, and there was definitely no code, I looked, and took an extra lap just to watch for it or any other codes. This also did not feel like how it felt when I did have the STVA failure, nor did that failure cause engine noise, I just lost a bunch of power immediately.

Since I am already in the cylinder head, do you guys think I should change out the valve guide seals too? I am looking at probably about 3-500 bucks in parts to rebuild my cylinder head depending on what I decide to replace, and it would sure be nice to never have to come back in here ever again (or at least for the longest possible time).

Today I am going to hunt down a valve spring compressor tool to get this apart.

Any other recommendations while I am in here?
Thanks guys

-Mike

Reactions: 1

alexei

· #14 · 18 d ago

Is the clutch basket loose?

SparkyMJ

Discussion Starter · #15 · 18 d ago

I thought that at one point too. The sound doesn't seem to come from the clutch, but I was wondering if some of the vibration might be the clutch basket being out of balance. I asked that on a separate thread on here a while ago, and the general consensus was that essentially no factory clutch basket is out of balance enough to cause real issues. I thought I might have had the clutch chattering, but the sounds and vibrations have nothing to do with the clutch condition or operation. It vibrates and rattles just the same with clutch in, clutch out, any gear including neutral, riding the clutch, before and after the two times I worked on the clutch and changed parts out, etc.

I am quite sure the sounds originate from my cylinder head. I have the head off and valves all out already too.

My machine shop is going to measure my valve spring force over this weekend, and I am hoping that the springs are my main issue, but I am also going to investigate the valve guide wear, and see if my shop can also get my seats re-cut while I am in here.

I also noticed a little residue around my intake boots on the cylinder head, so hopefully my motor wasn't sucking air in through the intake, but that could have also caused high RPM power loss due to leaning out. So I am going to replace those and their gaskets as well, just in case. But I feel like the leaning out and power loss still doesn't explain the rattling/pinging sounds coming from my engine, even before I had the high RPM issues.

Hopefully the proof is in the measurements, and it will then also run hopefully better once I re-seal the intakes. I am wondering if the intakes leaking may actually have been the real issue I had at the track causing my power issues, this sounds more likely than sudden head components failing...

I'll update what I find and what my shop finds. Thanks for the input.

-Mike

See less See more

SparkyMJ

Discussion Starter · #16 · 18 d ago

Any suggestions for cleaning the Titanium valves folks? Sounds like certain solvents and abrasives are not good for them, but some folks recommend red scotch brite pads and WD40 or something similar. I just have some carbon on the valves I want to get off for reassembly.

Thoughts?

-Mike

SparkyMJ

Discussion Starter · #17 · 14 d ago

I ended up buying a used cylinder head locally with only 12k miles on it. I am in the process of cleaning it up, inspecting, repairing the gasket surfaces, and all that fun stuff. It was cheap, but fingers crossed the valve seats and sealing surfaces on the valves themselves look better than mine. It came out of a motor that threw a rod, but looks like nothing hit the head... If its trash, I think my buddy who runs the salvage yard will take it back.

As long as the valves and seats are in better condition, and the guides aren't as worn, it should be clean up and install.

I did do the water leak test on the valves, and unfortunately cylinder #4 does have an intake valve leak. But, the parts were covered in gunk during the salvage, so there might just be some carbon stuck in the sealing surface, so I am going to take the valves out and clean it up and test again. Worst case, if this is the only issue, I can foot the bill for one seat cut or a new valve if needed. I will take my measurements once I can get my hands on a spring compressor again.

This is kinda a tough position. A true "valve job" by the book would be insanely expensive. Each titanium valve is like $90-100 I think, so if you really got to a high mileage and needed all 16, you need like $1500 in valves, and then my local machine shop quoted me $650 to install new guides and cut new seats, without parts cost. Man, what the heck. So if you need a full valve job it's like 2k. And odds are if you got to such a high mileage that you need it, the bike isn't worth pouring 2k into a valve job.

I kind of want to still do the work on my old cylinder head for the experience, but if I didn't or decide not to, is my old head just basically trash? Should I get it ported and polished if I am going to do anything with it at all? Then just throw in some crazy cams, springs, and do the whole thing? Are those steel valve kits from GSXR Zone worth anything at all?

Seems like a pickle if you're not made of money... Thoughts?

-Mike

See less See more

Reactions: 1

SparkyMJ

Discussion Starter · #18 · 14 d ago

Well crap. The book has a typo. Turns out the "valve wobble" to measure guide wear is misprinted, and I am naïve to have taken the number for face value. It says the deflection limit is 0.001". That's insanely small, less than it is when new. It says 0.25mm also, which of course, turns out to be 0.010".

Guess I wasted my money on a new cylinder head for no reason. Not the first typo in the 750 shop manual... Uhg. Hope I find out my springs were the issue I was having, waiting for my machine shop to get back to me on those...

-Mike

alexei

· #19 · 14 d ago

Cleaning the valves, wouldn't a good soak in diesel work? I wouldn't use solvents that would otherwise affect seal life, particularly acetone. Or, anything that's meant for cutting (sanding pads, scotch brite etc)

https://multimedia.3m.com/mws/media/2010476O/scotch-brite-nonwoven-abrasives-product-guide-high-resolution.pdf

See less See more

alexei

· #20 · 14 d ago

SparkyMJ said:
Well crap. The book has a typo. Turns out the "valve wobble" to measure guide wear is misprinted, and I am naïve to have taken the number for face value. It says the deflection limit is 0.001". That's insanely small, less than it is when new. It says 0.25mm also, which of course, turns out to be 0.010".

Guess I wasted my money on a new cylinder head for no reason. Not the first typo in the 750 shop manual... Uhg. Hope I find out my springs were the issue I was having, waiting for my machine shop to get back to me on those...

-Mike

Now you have 2 good heads.

1 - 20 of 21 Posts